Vehicle wheel balancer system

ABSTRACT

A method for determining weight display thresholds for static and dynamic imbalances and correction weights on a rotating body such as a vehicle wheel assembly, which vary with parameters of the rotating body, wheel and/or tire, and for displaying measured imbalances in relation to determined imbalance thresholds.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of, and claims priority to, U.S.patent application Ser. No. 10/648,165 filed on Aug. 26, 2003, now U.S.Pat. No. 6,952,964 which was a continuation-in-part of, and claimedpriority from, U.S. patent application Ser. No. 10/455,623 filed on Jun.5, 2003, now abandoned, both of which are hereby incorporated byreference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

BACKGROUND OF THE INVENTION

The present invention relates generally to automotive service equipmentdesigned to measure imbalance in a vehicle wheel assembly, and inparticular, to an improved wheel balancer system configured to adjust animbalance correction threshold level and to check centering of wheelsmounted to the wheel balancer system.

Wheel balancer systems are designed to determine characteristics of arotating body such as a wheel assembly consisting of a wheel rim and apneumatic tire, or of a wheel rim alone. The determined characteristicsinclude, but are not limited to static imbalances, dynamic imbalances,lateral forces, radial forces and runout parameters. Determination ofsome of these characteristics result from direct measurements, whileothers are obtained from an analysis of the mechanical vibrations causedby rotational movement of the rotating body. The mechanical vibrationsare measured as motions, forces, or pressures by means of transducersmounted in the wheel balancer system, which are configured to convertthe mechanical vibrations into electrical signals.

Existing wheel balancer systems suffer from subtle deficiencies inconnection with providing compensation for run-out and in tire to rimmatching procedures. These systems, such as the GSP9700 Seriesmanufactured by Hunter Engineering Co. of Bridgeton, Mo. are capable ofdisplaying an angular location at which a pneumatic tire should bemounted to a wheel rim to minimize an overall radial force variationassociated with the wheel assembly. For an accurate measurement of rimrunout at the beadseat of the tire, it is necessary for the rim runoutto be measured without the tire mounted thereon, and then for the rim tobe dismounted from the balancer, and the tire mounted to the rim. Thewheel assembly consisting of the tire and rim is then remounted to thebalancer to measure the force variations associated therewith. Anycentering difference with respect to the initial and subsequent mountingof the rim and wheel assembly on the balancer spindle will result inerrors in the determination of the rim runout, the assembly forcevariation, and the tire force variation computations. This “centeringerror” can become even more significant with larger wheel assembles,such as those currently entering the market.

There are many types of adaptors for use when mounting and centeringwheels onto a balancer spindle. Common examples of adaptors are cones,centering sleeves, flange plates with rigid pins, flange plates withcompliant pins, clamp cups and other devices as can be seen inpublications such as Hunter Engineering Company accessory brochure, FormNo. 3203T, entitled “Wheel Balancer Accessories”. Often there areseveral different adaptors that may be used to mount a wheel on a wheelbalancer. Due to variations in wheel design there are usually severaladaptors, or combinations of adaptors, that appear to fit the wheel, butactually do not center the wheel adequately on the wheel balancer shaft.Accordingly, it is desired to develop a solution to aid the operator inselecting the best adaptor for a wheel.

One solution to the centering error problem induced by the dismountingand remount of a wheel rim or wheel assembly on a balancer systemspindle is addressed in U.S. Pat. No. 6,481,282 B2 for “Wheel BalancerSystem With Centering Check”. The solution set forth in the '282 patentrequires that the wheel rim runout be measured before and after thewheel rim is dismounted from the balancer system, and a comparisoncarried out. If the comparison of the two runout measurements indicatesa difference which is greater than a predetermined threshold, it isassumed that the wheel rim has not been properly centered on thebalancer spindle during the remounting procedure, and a warning isprovided to the operator. The solution presented in the '282 patentfurther requires that the wheel balancer system include the capacity tomeasure and store wheel rim runout parameters (i.e. magnitude and phase)for subsequent comparisons with predetermined threshold values.

As not all wheel balancer systems are capable of measuring wheel rimrunout, it would be a particular advantage for a wheel balancer systemto incorporate a centering check process which does not require ameasurement of wheel rim runout both before and after altering thebalancer mounting of the of a wheel rim or wheel assembly.

While accurate centering of a wheel rim or wheel assembly on a balanceris important to obtain accurate measurements of any imbalance presenttherein, it is additionally important to provide an operator withinformation about whether or not there is a need to correct a detectedimbalance in the wheel rim or wheel assembly, or if the detectedimbalance is sufficiently small so as to have a negligible effect onvehicle performance and handling. Currently, wheel rim sizes in the U.S.market range from 13.0 inches in diameter up to and including thepresent DOT limit of 24.0 inches in diameter. It is anticipated thatwheel rim sizes will increase to 26.0 inches in diameter in the nearfuture, with a corresponding increase in associated tire sizes. Aproblem presented by the continued increase in wheel rim and wheelassembly sizes is the effect of a fixed imbalance correction thresholdlevel.

Due to the limited size increments in which imbalance correction weightsare available, conventional balancer systems are configured to displayas zero any required imbalance correction weight values below apredetermined threshold. Typically the predetermined threshold is 0.29oz., and is selected to be slightly greater than the smallest imbalancecorrection weight increment, regardless of the size of the wheel rim orwheel assembly. This can result in an operator “chasing” weights on asmall or narrow wheel due to the significant effect of the thresholdlevel on imbalances, and a poor balance on larger diameter wheels due toa reduced effectiveness of the threshold level. One solution is shown inU.S. Pat. No. 6,484,574 to Douglas, in which a balancer is configured toselect the best weight plane locations from data acquired by scanningthe rim profile. This is an advantageous method, but it is noteconomical for all balancers to have this feature.

Clearly, it would be further advantageous to provide a wheel balancersystem with a method for determining an imbalance correction thresholdlevel which varies in relation to the dimensions of the wheel assemblyundergoing balancing in addition to the incremental size of theimbalance correction weight employed, and which provides an operatorwith a scaled visual indication of any remaining imbalances presentafter application of suggested imbalance correction weights at suggestedweight placement locations.

BRIEF SUMMARY OF THE INVENTION

Briefly stated, in a first aspect of the present invention a method ofbalancing a rotating body includes the steps of mounting the body on aspindle of a balancer, measuring at least one imbalance parameter of thebody, altering the mounting of the body on the spindle of the balancer,obtaining a second measurement of the at least one imbalance parameterof the body, calculating a difference between said first measurement andsaid second measurement for said at least one imbalance parameter, andcomparing the calculated difference with a predetermined thresholdamount to determine whether the rotating body is properly centered onthe balancer spindle.

In a second aspect of the present invention, a method of balancing arotating body includes the steps of determining an imbalance correctionweight placement diameter and an imbalance correction weight placementseparation distance, utilizing the determined placement diametertogether with a predetermined imbalance force limit to identify a staticimbalance threshold, and utilizing the determined separation distanceand weight placement diameter together with a predetermined imbalancemoment limit to identify a dynamic imbalance threshold.

In a third aspect of the present invention, a method of balancing arotating body includes the steps of determining one or more imbalancecharacteristics of the rotating body, identifying one or more imbalancecorrection weight amounts and placement locations, and providing ascaled visual display of any imbalance present in the rotating bodyprior to, or following, application of the one or more imbalancecorrection weight amounts at the identified placement locations.

The foregoing and other objects, features, and advantages of theinvention as well as presently preferred embodiments thereof will becomemore apparent from the reading of the following description inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the accompanying drawings which form part of the specification:

FIG. 1 is a diagrammatic view illustrating a generic wheel balancersuitable for use with the present invention;

FIG. 2 is a simplified top plan view illustrating an alternate genericwheel balancer suitable for use with the present invention;

FIG. 3 is a block diagram illustrating various parts of a generic wheelbalancer of FIG. 1 or FIG. 2;

FIG. 4 is a flow chart diagram of a method of the present invention forcentering a rotating body on a balancer spindle;

FIG. 5 is a representation of a prior art balancer display indicating norequired weight placement for a rotating body of specific dimensions;

FIG. 6 is a representation of a prior art balancer display similar toFIG. 5, indicating a required weight placement for the rotating bodywith smaller diameter dimensions but having the same imbalance;

FIG. 7 is a representation of a prior art balancer display indicatingrequired weight placement for a rotating body of specific dimensions;

FIG. 8 is a representation of a prior art balancer display similar toFIG. 7, indicating no required weight placements for the rotating bodywith larger width (weight plane separation) dimensions but having thesame imbalance;

FIG. 9 is a flow chart diagram of a method of the present invention fordisplaying desired correction weights;

FIG. 10A is a two dimensional graphical representation of the blindamount versus wheel diameter for a predetermined static imbalance limit;

FIG. 10B is a surface plot representation of the blind amount comparedwith wheel diameter and tire diameter for a predetermined staticimbalance limit;

FIG. 11A is a surface plot representation of wheel rim diameter, wheelwidth, and couple blind amount for a predetermined couple imbalancelimit;

FIG. 11B is a surface plot similar to FIG. 11A, for tire diameter, wheelwidth, and couple blind amount for a predetermined couple imbalancelimit;

FIG. 12 is a representation of a display of the present inventionshowing a graphical presentation of the imbalance forces in the rotatingbody;

FIG. 13 is a representation of a display similar to FIG. 12, indicatingthat no additional weight is required on the wheel with a smallerdiameter dimension and having the same imbalance;

FIG. 14 is a representation of a display of the present inventionshowing a graphical presentation of the imbalance forces in the rotatingbody; and

FIG. 15 is a representation of a display similar to FIG. 12, indicatingthat less weight is required on a wheel with larger width (weight planeseparation) dimensions but having the same imbalance.

Corresponding reference numerals indicate corresponding parts throughoutthe several figures of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following detailed description illustrates the invention by way ofexample and not by way of limitation. The description clearly enablesone skilled in the art to make and use the invention, describes severalembodiments, adaptations, variations, alternatives, and uses of theinvention, including what is presently believed to be the best mode ofcarrying out the invention.

Turning to the drawings, FIG. 1 illustrates, in simplified form, themechanical aspects of a wheel balancer 10 suitable for the presentinvention. The particular balancer shown is illustrative only, since theparticular devices and structures used to obtain dimensional andimbalance information related to a rotating body could be readilychanged without changing the present invention.

Balancer 10 includes a rotatable shaft or spindle 12 driven by asuitable drive mechanism such as a motor 14 and drive belt 16. Mountedon spindle 12 is a conventional optical shaft encoder 18 which providesspeed and rotational position information to the central processing unit20, shown in FIG. 3.

During the operation of wheel balancing, at the end of the spindle 12, arotating body 22 under test is removably mounted for rotation with thespindle hub 12A. The rotating body 22 may comprise a wheel rim, or awheel assembly consisting of a wheel rim and a tire mounted thereon. Todetermine the rotating body imbalance, the balancer includes at least apair of imbalance force sensors 24 and 26, such as piezoelectric sensorsor strain gauges, coupled to the spindle 12 and mounted on the balancerbase 28.

Turning to FIG. 2, it can be seen that the actual construction of themechanical aspects of the balancer 10 can take a variety of forms. Forexample, the spindle 12 can include a hub 12A against which the rotatingbody 22 abuts during the balancing procedure.

When a rotating body 22 is unbalanced, it vibrates in a periodic manneras it is rotated, and these vibrations are transmitted to the spindle12. The imbalance sensors 22 and 24 are responsive to these vibrationsin the spindle 12, and generate a pair of analog electrical signalscorresponding to the phase and magnitude of the vibrations at theparticular sensor locations. These analog signals are input to thecircuitry of FIG. 3, described below, which determines the requiredmagnitudes and positions of correction weights necessary to correct theimbalance.

Turning to FIG. 3, wheel balancer 10 includes not only the imbalancesensors 22 and 24, and spindle encoder 18, but also the centralprocessing unit 20 (such as a microprocessor, digital signal processor,or graphics signal processor). the central processing unit 23 performssignal processing on the output signals from the imbalance sensors 22and 24 to determine an imbalance in the rotating body. In addition, thecentral processing unit 20 is connected to and controls a display 30which provides information to an operator, control motor 14 throughassociated motor control circuits 32, and keeps track of the spindlerotation position with encoder 18.

Balancer 11 further includes one or more manual inputs 34, such as akeyboard, control knobs, or selector switches, which are connected tothe central processing unit 20. The central processing unit 20 hassufficient capacity to control, via software, all the operations of thebalancer 10 in addition to controlling the display 30. The centralprocessing unit 20 is connected to a memory such as an EEPROM memory 36,EPROM program memory 38, and a dynamic RAM (DRAM) memory 40. The EEPROMmemory 36 is used to store non-volatile information, such as calibrationdata, while the central processing unit 20 uses the DRAM 40 for storingtemporary data.

The central processing unit 20 is also connected to an analog-to-digitalconverter 42. The signals from the imbalance sensors 22 and 24 aresupplied through anti-aliasing circuitry 44A and 44B (if needed) to theanalog-to-digital converter 42.

The operation of the various components described above is fully setforth in U.S. Pat. No. 5,396,436, the disclosure of which isincorporated herein by reference. It should be understood that the abovedescription is included for completeness only, and that various othercircuits could be used instead.

In a first embodiment of the present invention, the balancer 10 isconfigured with software to provide an operator with an option toperform a centering check to ensure that the rotating body 22 isaccurately mounted to the spindle 12. As shown in FIG. 4, after mountingthe rotating body 22 on the balancer spindle (Box 100), and an initialmeasurement of at least one imbalance parameter, such as a raw forcetransducer output, an imbalance magnitude, an imbalance angularlocation, or the mass of the rotating body, is obtained (Box 102), thecentering check is performed by first loosening a wing nut or othermounting device securing the rotating body 22 to the spindle 12. Withthe mounting device loosened, the mounting of the rotating body 22 aboutthe spindle is altered (Box 104), and the wing nut or other mountingdevice retightened. The altering of the mounting may involve eitherremoving the rotating body 22 from the spindle 12 and replacing itthereon, or simply rotating the rotating body 22 about the axis of thespindle 12.

With the rotating body 22 in the altered mounting position, a secondmeasurement of the previously measured, at least one imbalanceparameters is conducted (Box 106). The central processing unit 20compares the previous measurements with the second measurements takenafter the altering of the rotating body mount on the spindle 12 toidentify a difference between the two measurements (Box 108). Thecalculated difference is then compared with a predetermined threshold ortolerance (Box 110). If the results of the comparison indicate themeasurements deviate by more than a predetermined amount (Box 112), thecentral processing unit 20 causes a message to be shown on the display30 warning of a detected mis-centering of the rotating body 22 on thespindle 12.

To correct a mis-centering of the rotating body 22 on the spindle 12,the central processing unit 20 provides directions to the operator ondisplay 30, requesting that the operator repeat the step of altering themounting of the rotating body 22 on the spindle 12. Once the rotatingbody 22 is re-mounted on the spindle 12 in an altered position, thecentral processing unit obtains an additional measurement of thepreviously measured imbalance parameters. This process is repeated untilthe results of a comparison of the most recently obtained measurementsand any previously obtained measurements do not deviate by more than apredetermined amount, i.e. indicating that the rotating body 22 iscentered to within the predetermined tolerance (Box 114).

The principle reasoning behind the centering check methodology set forthabove is that an operator is more likely to properly center the rotatingbody 22 on the spindle 12 at least twice, and less likely that anoperator will mis-center the rotating body 22 twice in the same way,producing nearly identical measurements of the imbalance parameters.Hence, the central processing unit is configured to consider therotating body 22 to be properly centered upon the spindle 12 the firsttime the results of the comparison do not indicate a deviation of morethan a predetermined amount between the most recent measurement and anyprevious measurements of the imbalance parameters.

Optionally, the central processing unit 20 may be configured toterminate the centering check procedure, and provide a suitable warningon display 30 to the operator if a predetermined number of mis-centeredmountings are detected in sequence. If an operator is unable to properlycenter the rotating body 22 on the spindle 12 within a predeterminednumber of tries, it is likely that the centering deviations are not theresult of operator mounting error, but rather, are the result of damageto the rotating body 22, spindle 12, or mounting device, or possibly thewrong adaptor is selected to be used to secure the rotating body 22 tothe spindle 12.

In an alternate embodiment of the present invention for use when therotating body 22 is a wheel rim and tire assembly, the runout of thetire mounted on the wheel rim is obtained in place of the measurement ofthe imbalance parameter. This runout measurement may be made by a devicethat contacts the outermost diameter of the tire as the tire rotates.For example, an arm with a roller secured thereto, such as is providedwith the Hunter GSP9700, or an arm with a fixed surface disposed on theend. Alternatively, the tire outer diameter can be measured by aconventional non-contact tire measurement device, such as an ultrasonicsensor, a laser, or a capacitive proximity sensor. Also alternatively,the lateral runout of the tire sidewall, or any surface on the side ofthe assembly, can be measured (by a contacting device, or non-contactingdevice) instead of, or in addition to, radial runout.

After an initial measurement of the tire runout is obtained and stored,the centering check is performed by first loosening a wing nut or othermounting device (not shown) securing the rotating body 22 to the spindle12. With the mounting device loosened, the mounting of the rotating body22 about the spindle is altered, and the wing nut or other mountingdevice (not shown) retightened. The altering of the mounting may involveeither removing the rotating body 22 from the spindle 12 and replacingit thereon, or simply rotating the rotating body 22 about the an axis ofthe spindle 12.

With the rotating body 22 in the altered mounting position, a secondmeasurement of the previously measured tire runout is conducted. Thecentral processing unit 20 compares the previous measurements with thesecond measurements taken after the altering of the rotating body mounton the spindle 12. If the results of the comparison indicate themeasurements deviate by more than a predetermined amount, where thepredetermined amount may be a constant or a variable based on wheel/tiresize, mass or other parameter, the central processing unit 20 causes amessage to be shown on the display 30 warning of a detectedmis-centering of the rotating body 22 on the spindle 12, so thatsuitable corrective action may be taken by the operator.

Once a rotating body 22 is accurately centered on the balancer spindle12, the balancer 10 can begin the process of measuring one or moreimbalance parameters of the rotating body 22, and providing the operatorwith one or more suggested imbalance correction weight magnitudes andplacement locations. Imbalance correction weight magnitudes andplacement locations are calculated and displayed to an operator on ascreen or numerical readout 30. Due to the limited size increments inwhich imbalance correction weights are usually available, conventionalbalancer systems are configured to display to the operator a zero valuefor any imbalance which would require the installation of an imbalancecorrection weight amount which is below a predetermined threshold.

Typically the predetermined threshold is selected to be slightly greaterthan the smallest imbalance correction weight increment, regardless ofthe size of the wheel rim or wheel assembly. For a system adapted to useimbalance correction weights having 0.25 oz. increments, an exemplarythreshold limit is 0.29 oz. of imbalance. This can result in an operator“chasing” weights on a small or narrow wheel due to the insignificanteffect of the threshold level on imbalances, and a poor balance onlarger diameter wheels.

For example, as shown in FIG. 5, a wheel having a 6.0 inch axial width,and a 15.0 inch diameter might require imbalance weights below thepredetermined weight threshold, resulting in the balancer displaying toan operator that no imbalance correction weights are required for eitherthe left or right imbalance correction planes. However, as shown in FIG.6, if the dimensions of the wheel are manually changed by the operatorusing the “SET DIMENSIONS” button 150 to indicate a 5.0 inch axial widthand a 14.0 inch diameter, without re-measuring the wheel imbalance,larger weights are displayed to correct the imbalance, which exceed thepredetermined weight threshold level. As a result, a conventionalbalancer would now direct an operator to install weights in the left andright imbalance correction planes (as indicated by arrows 152) despitethe fact that the amount of the imbalance is unchanged.

A similar problem exists for conventional balancer systems whenbalancing large wheels. For example, as shown in FIG. 7, a wheel havingan 8.0 inch axial width, and a 16.0 inch diameter might have animbalance above the predetermined weight threshold, resulting in thebalancer displaying to an operator that imbalance correction weights arerequired for both the left or right imbalance correction planes.However, as shown in FIG. 8, if the dimensions of the wheel are manuallychanged by the operator using button 150 to show an 18.0 inch diameter,without re-measuring the wheel imbalance, less weight is displayed tocorrect the imbalance, which drops below the predetermined weightthreshold level. As a result, a conventional balancer would now indicateto an operator that no weights in the left and right imbalancecorrection planes are required, despite the fact that the amount of theimbalance is unchanged.

In an alternate embodiment of the present invention, the balancer 10 isprovided with a predetermined value representative of the maximumimbalance effect which is permitted for each type of imbalance in therotating body 22 to be corrected, i.e., for static imbalance and fordynamic imbalance. For example, a predetermined static imbalance momentlimit is provided to identify a static imbalance threshold, and apredetermined dynamic imbalance moment limit is provided to identify adynamic imbalance threshold. Preferably, the predetermined limits areselected to correspond to a level of imbalance moments in the rotatingbody 22 which are imperceptible to the average consumer, such as 2.18oz.-in. for a static imbalance moment limit, corresponding to a 0.29 oz.weight on a 15″ diameter wheel rim, and 15.0 oz.-in². for a dynamicimbalance limit which corresponds to approximately a 0.33 oz. weight ona 6″ wide, 15″ diameter wheel rim. It may be desirable, however, toadjust these limits to favor either static imbalance or dynamic (couple)imbalance. For instance, it is understood that passengers in a vehicleare less sensitive to a dynamic (couple) imbalance than a staticimbalance. A way to reduce technician's labor with a minimal increase invibration would be to increase the dynamic limit to 20.0 oz.-in.².

In a second alternate embodiment of the present invention, shown in FIG.9, a balancer 10 is configured to select an imbalance correction weightdisplay threshold based upon one or more dimensions of the rotating body22 being balanced. These dimensions include the imbalance correctionweight placement diameter and an imbalance correction weight placementseparation distance. Preferably, these dimensions are measured directlyby the balancer 10 utilizing operator assistance to place a measuringdevice, such as a dataset arm, at the desired imbalance correctionweight planes and/or at the edge of the rotating body 22. Alternatively,when the diameter and width of a rotating body 22 are known, an operatorcan directly supply the balancer 10 with corresponding values using oneor more manual inputs 34 (Box 200).

The balancer 10 is configured to utilize the predetermined valuerepresentative of the maximum imbalance effect permitted, together withthe associated dimensions of the rotating body 22 to identify a variableimbalance correction threshold used to display, to an operator ondisplay 30, as zero any imbalance which would require an imbalancecorrection weight value below the variable threshold. (Box 204).

For correcting static imbalances present in the rotating body 22 (Box206), the predetermined static imbalance moment limit is F_(max)(typically in units of oz.-in.), the known or measured rotating bodydiameter is D, and the imbalance correction threshold or “blind” isW_(BS). A variable threshold value for W_(BS) is determined by thebalancer 10 according to the following equation:W _(BS) =F _(MAX)/(D/ ₂)  Equation (1)

For correcting dynamic imbalances present in the rotating body 22 (Box208), the predetermined dynamic imbalance moment limit is M_(max),(typically in units of oz.-in.²) the known or measured rotating bodyaxial length or axial width is W, and the imbalance correction thresholdor “blind” is W_(BD). If it is assumed that there is no static imbalancein the wheel, a variable threshold value for W_(BD) is determined by thebalancer 10 according to the following equation:W _(BD) =M _(max) /W*(D/2)  Equation (2)

For example, if the balancer 10 is configured with a predeterminedstatic imbalance moment limit (F_(max)) of 2.18 oz.-in. for correctingstatic imbalances present in the rotating body 22, and the rotating body22 has a measured or known diameter of 15.0″, solving Equation (1) abovefor W_(BS) yields an imbalance correction threshold or “blind” of 0.29oz. If the rotating body 22 has a measured or known diameter of 12.0″,Equation (1) yields an imbalance correction threshold or “blind” of 0.36oz. Correspondingly, if the rotating body 22 has a measured or knowndiameter of 20.0″, Equation (1) yields an imbalance correction thresholdor “blind” of 0.21 oz. for the same value of F_(max).

The benefit offered by a balancer 10 configured to utilize theaforementioned methods to identify imbalance correction thresholds basedin-part upon the known or measured dimensions of a rotating body 22undergoing balancing can be clearly illustrated by the followingcomparisons.

When balancing a wheel assembly having a 15.0″ diameter wheel rim withan axial width of 5.0″, it is possible for a conventionally configuredbalancer to identify a static imbalance over the limit of 2.18 oz.-in.but a dynamic couple under the limit of 15 oz.-in.² and suggest acorrection requiring two imbalance correction weights of 0.25 oz. and0.75 oz., one to be placed on the inner lip of the wheel rim, and theother to be placed on the outer lip of the wheel rim. However, on abalancer 10 configured with a predetermined dynamic imbalance momentlimit (M_(max)) of 15.0 oz.in², the dynamic couple is determined to haveminimal effect on the vehicle and will be ignored and the remainingstatic imbalance can be corrected by a single 0.25 oz. weight.

By setting the imbalance threshold amounts based on the actual force andmoment values, rather than displayed weight amounts, it is possible tominimize the residual imbalance in a wheel. A conventional balancer maymeasure a purely static imbalance that requires 0.50 oz. weight tocorrect. If the balancer is set to the “Dynamic” balance mode it willcalculate that a 0.25 oz. weight is required on both the left and theright planes. Since the traditional threshold is set to 0.29 oz. themachine will show that no correction weights are required, but the wheelis not balanced. With the method of the present invention employed, thecorrect weights will be displayed and the wheel will be properlybalanced. In the example described above, there is a small amount ofcouple imbalance present along with the static imbalance. Even thoughthe amount of couple is small and no specific weights are required tocorrect it, it is possible to place the static correction weight in alocation to possibly reduce the couple imbalance.

When correcting the static imbalance, the single static weight can beplaced on either the inner plane, adjacent the balance, or the outerplane, opposite the balancer. The inner plane is alternatively referredto as the left plane, when the wheel is mounted on the right side of abalancer, and the outer plane is alternatively referred to as the rightplane for the same wheel placement. To choose the correct plane in whichto place the single static weight, it is necessary to compare the phaseof the dynamic couple vector to the phase of the static force vector.The static correction weight is placed on the plane that minimizes theresidual dynamic couple imbalance, without the placement of additionalcouple imbalance correction weights.

This will correct the static imbalance (which was greater than theblind), and depending upon the difference between the couple and staticimbalance phase, it will decrease the couple imbalance or leave itunchanged (couple imbalance was already acceptably low). Since the innerand outer plane couple imbalance phases are always 180 degrees apart,the static imbalance phase will never be more than 90 degrees away fromone of the couple imbalance phases. If the difference between the staticand one of the couple imbalance phases is small, there will be asignificant improvement in couple imbalance. If the static imbalancephase is exactly 90 degrees between both couple imbalance phases, thecouple imbalance will not change when the static correction weight isadded. This can be accomplished by the following logic sequence:

Assume the balancer is in “Dynamic” mode, static imbalance is greaterthan blind, and couple imbalance is less than the predetermined blind.The following steps are taken to place a single weight that will correctthe static imbalance while reducing (or not changing) the coupleimbalance.

Let couple imbalance=0 and calculate the static correction weight.

Static weight magnitude=Static imbalance/radius

Static weight phase=Static imbalance phase+180 degrees.

To correct the static imbalance, this weight could be placed on eitherthe inner plane or the outer plane.

If the difference between the static imbalance phase angle and the outerplane couple imbalance phase angle is less than 90 degrees, place thesingle static correction weight on the outer plane. Otherwise, place theweight on the inner plane.

If the balancer is in “Static” mode it is common that dimensions willonly be entered for a single plane. With the present invention it isdesirable to compare the absolute dynamic couple imbalance to thedynamic couple threshold. If the absolute dynamic couple exceeds thethreshold it is desirable to provide an indicator to the operator ofthis condition. The indication may be in the form of blinking lights,alpha-numeric text, or in the form of a message. If the operator hasentered dimensions for two planes the indicator may be in the form of adisplay of the weights required to correct the couple imbalance.

To aid an operator in determining if a rotating body 22 has beenbalanced to within a predetermined threshold for both static imbalanceand dynamic imbalance, the balancer 10 in an alternate embodiment isconfigured to provide the operator with a graphical illustration 300 ofthe measured imbalances relative to the threshold level of absoluteimbalances on display 30, i.e. the couple imbalance threshold and thestatic imbalance threshold. Conventionally, such as shown in U.S. Pat.No. 5,915,274 to Douglas, weights required to correct static and dynamicimbalances are displayed relative to a fixed weight amount threshold toan operator on a bar graph. The fixed weight amount is based on theincremental weight size and the vehicle wheel geometry. In contrast, thegraphical illustration 300 of the present invention displays informationto an operator based upon absolute imbalances, and not on theincremental weight sizes and vehicle wheel geometry.

Turning to FIGS. 12 and 13, a display 30 from a balancer 10 configuredwith the features of the present invention is shown first for a wheelhaving an axial length or width of 6.0 inches and a diameter of 15.0inches. In this example, the imbalance present in the wheel for bothstatic and dynamic imbalance is below a threshold level. This isillustrated with the graphical illustration 300, incorporating a slidingscale 302 for static imbalance, and a sliding scale 304 for dynamicimbalance. On each sliding scale 302 and 304, shown in FIG. 12, thecomputed imbalance amounts, as indicated by the arrows 306S and 306D,fall within the acceptable range, hence no imbalance correction weightamounts are indicated for the left and right correction planes. Further,as shown in FIG. 13, if the dimensions of the wheel are manually changedby the operator to indicate a 5.0 inch axial with and a 14.0 inchdiameter, (corresponding to the change shown in FIG. 6) withoutre-measuring the imbalance, the measured imbalance in the wheel remainsunchanged, as shown on the sliding scales 302 and 304. As a result, noimbalance correction weight amounts are indicated for the left and rightcorrection planes.

The method of the present invention provides a similar advantage whenbalancing large wheels. For example, as shown in FIG. 14, a wheel havinga 8.0 inch axial width, and a 16.0 inch diameter might have an imbalanceabove the threshold, as shown on sliding scales 302 and 304, resultingin the balancer displaying to an operator imbalance correction weightsrequired for both the left and right imbalance correction planes.However, as shown in FIG. 15, if the dimensions of the wheel aremanually changed by the operator to show an 18.0 inch diameter, withoutre-measuring the imbalance, less weight is required to correct the sameimbalance. As a result, the balancer indicates to an operator thatreduced weights in the left and right imbalance correction planes arestill required to correct the imbalance which is above the imbalancethreshold.

It is known that a rotating body 22 static imbalance force is a functionof the imbalance mass, the radial distance of the imbalance mass fromthe axis of rotation, and the angular velocity of the rotating body 22.In a vehicle wheel application, where the rotating body 22 consists of awheel rim and tire assembly, for any given vehicle speed, the angularvelocity may be expressed as a function of the tire diameter or as afunction of the tire diameter and the wheel rim diameter. Hence, in analternate embodiment of the present invention, the imbalance force F,experienced by a vehicle from a rotating wheel assembly may be definedas:

$\begin{matrix}{F = \frac{\left( \frac{v}{\pi\; D_{t}} \right)^{2}{mD}_{W}}{2}} & {{Equation}\mspace{14mu}(3)}\end{matrix}$

where v is the vehicle velocity, D_(T) is the tire diameter, D_(W) isthe correction weight application diameter, which is equal to the wheeldiameter for clip-on weights, and m is the imbalance mass. For example,if an acceptable imbalance correction threshold or “blind” for a wheelrim having a diameter D_(W0) of 15.0″ with a tire having a diameterD_(T0) of 28.0″ is 0.29 oz. (m₀), an equation for calculating anequivalent “blind” (m₁) for an assembly with the dimensions D_(W1) andD_(T1) is:

$\begin{matrix}{m_{1} = {\frac{m_{0}D_{W\; 0}}{D_{W\; 1}}\left( \frac{D_{T\; 1}}{D_{T\; 0}} \right)^{2}}} & {{Equation}\mspace{14mu}(4)}\end{matrix}$

Once an acceptable imbalance correction threshold or “blind” isestablished for a particular tire and rim combination, an equivalentimbalance correction threshold or “blind” may be automaticallycalculated using Equation (4) for a wide variety of wheel assemblies,providing an imbalance correction threshold curve, such as shown in FIG.10A for wheel rim dimensions and in FIG. 10B for tire dimensions.

Utilizing the tire diameter D_(T), and the wheel diameter D_(W), wheelassemblies may be classified into predefined groupings. For example,performance wheel assemblies where D_(T)−D_(W) is relatively small (˜3.0inches or less), touring wheel assemblies, where D_(T)−D_(W) is between3.0″ and 5.0″, and truck wheel assemblies, where D_(T)−D_(W) is greaterthan 5.0″. Each different predefined grouping may be provided with adifferent acceptable imbalance correction threshold or “blind” curve.Using Equation (4), the specific imbalance correction threshold or“blind” for a wheel assembly having specific dimensions may beautomatically calculated, once a specific tire grouping and associatedcurve has been selected.

A similar analysis for the rotating body 22 couple imbalance force canbe made. Where L is the wheel width, the imbalance couple (M) felt bythe vehicle can be expressed as:

$\begin{matrix}{M = {\left( \frac{v}{\pi\; D_{T}} \right)^{2}{wL}\frac{D_{W}}{2}}} & {{Equation}\mspace{14mu} 5}\end{matrix}$

If an acceptable imbalance correction threshold or “blind” for a wheelassembly having a 15×6 inch wheel rim (D_(W0)×L₀), with a 28.0 inchdiameter tire (D_(T0)) installed thereon is 0.29 oz (w₀) then usingEquation 5, and equivalent blind (w₁) for an assembly with the dimensionD_(W1), D_(T1), and L₁ is:

$\begin{matrix}{w_{1} = {\frac{w_{0}D_{w\; 0}}{D_{w\; 1}}\left( \frac{D_{T\; 1}}{D_{T\; 0}} \right)^{2}\frac{L_{0}}{L_{1}}}} & {{Equation}\mspace{14mu} 6}\end{matrix}$

Once an acceptable couple imbalance correction threshold or “blind” isestablished for a particular tire and rim combination, an equivalentcouple imbalance correction threshold or “blind” may be automaticallycalculated using Equation (6) for a wide variety of wheel assemblies,providing an couple imbalance correction threshold curve, such as shownin FIG. 11A for wheel rim dimensions and FIG. 11B for tire dimensions.

The present invention can be embodied in-part in the form ofcomputer-implemented processes and apparatuses for practicing thoseprocesses. The present invention can also be embodied in-part in theform of computer program code containing instructions embodied intangible media, such as floppy diskettes, CD-ROMs, hard drives, or another computer readable storage medium, wherein, when the computerprogram code is loaded into, and executed by, an electronic device suchas a computer, micro-processor or logic circuit, the device becomes anapparatus for practicing the invention.

The present invention can also be embodied in-part in the form ofcomputer program code, for example, whether stored in a storage medium,loaded into and/or executed by a computer, or transmitted over sometransmission medium, such as over electrical wiring or cabling, throughfiber optics, or via electromagnetic radiation, wherein, when thecomputer program code is loaded into and executed by a computer, thecomputer becomes an apparatus for practicing the invention. Whenimplemented in a general-purpose microprocessor, the computer programcode segments configure the microprocessor to create specific logiccircuits.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results are obtained. Asvarious changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

1. A method for displaying, on a balancer, an imbalance of a rotatingbody, comprising the steps of: establishing a static imbalance thresholdassociated with an acceptable static imbalance of the rotating body;establishing a dynamic imbalance threshold associated with an acceptabledynamic imbalance of the rotating body; calculating both a staticimbalance and a dynamic imbalance of the rotating body having an unknownimbalance; and providing a display of a relationship between saidcalculated static imbalance and said associated established staticimbalance threshold to an operator together with a display of arelationship between said calculated dynamic imbalance and saidassociated established dynamic imbalance threshold to an operator. 2.The method of claim 1 for displaying an imbalance of a rotating bodywherein said step of establishing each of said imbalance thresholdsestablishes an imbalance threshold based on one or more dimensionalcharacteristics of the rotating body.
 3. The method of claim 1 fordisplaying an imbalance of a rotating body wherein said provided displayis a non-numeric display including a representation of said calculatedstatic imbalance relative to said establish static imbalance threshold,and of said calculated dynamic imbalance relative to said establisheddynamic imbalance threshold.
 4. A method for displaying, on a balancer,an imbalance of a rotating body, comprising the steps of: establishing astatic imbalance threshold and a dynamic imbalance threshold;calculating a static imbalance and a dynamic imbalance of the rotatingbody; and providing a display of said calculated static imbalance inrelation to said established static imbalance threshold to an operator,together with a display of said calculated dynamic imbalance in relationto said established dynamic imbalance threshold to an operator; andwherein the step of providing a display further includes generating ascaled representation of said calculated static imbalance and saidestablished static imbalance threshold together with a scaledrepresentation of said calculated dynamic imbalance and said establisheddynamic imbalance threshold, each of said displayed representationsscaled to fit within a display region.
 5. The method of claim 1 fordisplaying an imbalance of a rotating body wherein the step ofcalculating both a static and dynamic imbalance includes calculatingboth a static and dynamic imbalance remaining in the rotating bodyfollowing application of one or more known imbalance correction weightsat known positions.
 6. The method of claim 1 wherein said rotating bodyhaving an unknown imbalance includes at least a vehicle wheel rim. 7.The method of claim 4 wherein said rotating body having an unknownimbalance includes at least a vehicle wheel rim.
 8. The method of claim1 wherein an imbalance correction weight amount associated with saidestablished dynamic imbalance threshold is greater than an imbalancecorrection weight amount associated with said established staticimbalance threshold.
 9. The method of claim 1 wherein said calculatedstatic imbalance and said calculated dynamic imbalance are representedas imbalance forces.
 10. The method of claim 4 wherein an imbalancecorrection weight amount associated with said established dynamicimbalance threshold is greater than an imbalance correction weightamount associated with said established static imbalance threshold. 11.The method of claim 4 wherein said calculated static imbalance and saidcalculated dynamic imbalance are represented as imbalance forces.
 12. Avehicle wheel balancer system having a central processing unitoperatively coupled to receive imbalance data from imbalance sensors,and a display controlled by the central processing unit, comprising: amemory operatively coupled to the central processing unit, said memorystoring a static imbalance threshold for a vehicle wheel having anunknown imbalance undergoing an imbalance measurement procedure and adynamic imbalance threshold for said wheel; wherein the centralprocessing unit is configured to calculate both a static imbalance and adynamic imbalance of the vehicle wheel; and wherein the centralprocessing unit is further configured to control the display to presenta representation of a relationship between said calculated staticimbalance and said stored static imbalance threshold together with arepresentation of a relationship between said calculated dynamicimbalance and said stored dynamic imbalance threshold.
 13. The vehiclewheel balancer system of claim 12 wherein the central processing unit isfurther configured to scale each of said displayed representations tofit within a display region of said display.
 14. The vehicle wheelbalancer system of claim 12 wherein the central processing unit isconfigured to establish, for storage in said memory, said staticimbalance threshold and said dynamic imbalance threshold for the vehiclewheel.
 15. The vehicle wheel balancer system of claim 14 wherein thecentral processing unit is configured to establish each of saidthresholds based on one or more dimensional characteristics of thevehicle wheel.
 16. The vehicle wheel balancer system of claim 12 whereineach of said presented representations is non-numeric.